How to use the assetgraph.query function in assetgraph

/*
 * expush
 * https://github.com/Munter/expush
 *
 * Copyright (c) 2014 Peter Müller
 * Licensed under the MIT license.
 */

'use strict';

var fs = require('fs'),
    app = require('express')(),
    spdy = require('spdy'),
    async = require('async'),
    AssetGraph = require('assetgraph'),
    query = AssetGraph.query,
    mime = require('mime'),
    root = process.cwd(),
    chalk = require('chalk'),
    assetGraph = new AssetGraph({root: root + '/'});

// Self signed certs
var options = {
  key: fs.readFileSync(__dirname + '/../keys/server.key'),
  cert: fs.readFileSync(__dirname + '/../keys/server.crt'),
  ca: fs.readFileSync(__dirname + '/../keys/server.csr')
};

function sendAsset(asset, req, res, next) {
    var contentType = mime.types[asset.extension.substr(1) || 'application/octet-stream'],
        etag = '"' + asset.md5Hex + '"',
        ifNoneMatchHeaderValue = req.headers['if-none-match'];